The decrease in atp after death causes muscles become stiff in what is known as rigor mortis. why is the lack of atp causing stiffness?
a. because atp is needed to perform the power stroke
b. because atp is needed to in order to form a cross-bridge between actin and myosin
c. because atp is needed to displace troponin
d. because atp is needed to release the calcium ions from the sarcoplasmic reticulum
e. because atp is needed to break the cross bridge between actin and myosin

e. Because ATP is needed to break the cross bridge between actin and myosin

Explanation:

The energy for muscle contraction comes from ATP (adenosine triphosphate) molecules produced during cellular respiration. These molecules act on the binding of myosin to actin, causing muscle contraction.

ATP acts both on the binding of myosin to actin and on its separation, which occurs during muscle relaxation. When ATP is lacking, myosin stays attached to actin, causing muscle tightness. This is what happens after death, producing the state of rigor mortis.